1. Field of the Invention
The present invention relates to a liquid crystal display device and a method for producing the same. More specifically, the present invention relates to a liquid crystal display device having wide viewing angle characteristics and a method for producing the same.
2. Description of the Related Art
In the past, a liquid crystal display device (hereinafter, also referred to as an xe2x80x9cLCDxe2x80x9d) in a twisted nematic (TN) mode has been known. The liquid crystal display device in a TN mode has poor viewing angle characteristics (i.e., a narrow viewing angle). As shown in FIG. 30A, when TN-LCD 200 is in a gray-scale display, liquid crystal molecules 202 are tilted in one direction. As a result, in the case where TN-LCD 200 is observed in viewing angle directions A and B as shown in FIG. 30A, apparent light transmittance varies depending upon the direction. Accordingly, the display quality (e.g., contrast ratio) of TN-LCD 200 greatly depends upon the viewing angle.
In order to improve the viewing angle characteristics of a liquid crystal display device by controlling the alignment state of liquid crystal molecules, it is required to align liquid crystal molecules in at least two directions in each pixel. Examples of such liquid crystal display devices includes those in an axially symmetric aligned microcell (ASM) mode in which liquid crystal molecules are axis-symmetrically aligned in each pixel. Referring to FIG. 30B, for example, when a liquid crystal display device 210 in an ASM mode in which a liquid crystal region 214 is surrounded by a polymer region 212 is in gray scales, liquid crystal molecules are aligned in two different directions. In the case where the liquid crystal display device 210 is observed in viewing angle directions represented by arrows A and B, apparent light transmittance is averaged. As a result, the light transmittance in the viewing angle directions A and B becomes substantially equal, whereby viewing angle characteristics are improved compared with those in a TN mode.
Examples of liquid crystal display devices in a mode having improved viewing angle characteristics (hereinafter, referred to as a xe2x80x9cwide viewing angle modexe2x80x9d) including an ASM mode will be described below.
(1) There is a technique for electrically controlling a transparent state or an opaque state by utilizing birefringence of a liquid crystal material in a liquid crystal display device which has polymer walls in a liquid crystal cell without polarizing plates and which does not require any alignment treatment. According to this technique, the ordinary index of liquid crystal molecules is matched with the refractive index of a supporting medium. Under the application of a voltage, the liquid crystal molecules are aligned, whereby a transparent state is displayed. When no voltage is being applied, the alignment of the liquid crystal molecules is disturbed, whereby a light scattering state is displayed.
For example, Japanese National Phase PCT Laid-open Publication No. 61-502128 discloses a technique for mixing liquid crystal with a photocurable or thermosetting resin, curing the resin to phase-separate liquid crystal from the resin, thereby forming liquid crystal droplets in the resin. Furthermore, Japanese Laid-open Publication Nos. 4-338923 and 4-212928 disclose a liquid crystal display device in a wide viewing angle mode obtained by combining the device disclosed in Japanese National Phase PCT Laid-open Publication No. 61-502128 with polarizing plates in such a manner that polarization axes are orthogonal to each other.
(2) As a technique for improving viewing angle characteristics of a non-scattering type liquid crystal cell using polarizing plates, Japanese Laid-open Publication No. 5-27242 discloses a technique for producing a composite material containing liquid crystal and a polymer material from a mixture of liquid crystal and a photocurable resin by phase separation. According to this technique, the liquid crystal molecules in liquid crystal domains are randomly aligned by generated polymers, the liquid crystal molecules rise in different directions in each domain under the application of a voltage. Therefore, the apparent light transmittance observed in each direction becomes substantially equal (because retardation dxc2x7xcex94n is averaged, where d is a thickness of a liquid crystal layer and xcex94n is birefringence of a liquid crystal material), so that the viewing angle characteristics in gray scales are improved.
(3) Recently, in Japanese Laid-open Publication No. 7-120728, the inventors of the present invention have proposed a liquid crystal display device in which liquid crystal molecules are omnidirectionally aligned (e.g., in a spiral state) in pixel regions by controlling light using a photomask or the like during photopolymerization. This device uses a technique of axis-symmetrically aligning liquid crystal molecules by utilizing phase separation from a mixture of liquid crystal and a photocurable resin. The liquid crystal molecules are axis-symmetrically aligned when no voltage is being applied, and come closer to homeotropic alignment (alignment vertical to the substrates) under the application of a voltage, whereby the viewing angle characteristics are remarkably improved. This technique is a p-type display mode using a p-type liquid crystal material (i.e., a material with a positive dielectric anisotropy xcex94xcex5).
As an example of a method for producing a device as described above, Japanese Laid-open Publication No. 8-95012 discloses a method for forming lattice-shaped polymer walls having a thickness smaller than the cell thickness in each pixel region, injecting a mixture of liquid crystal and a photocurable resin into the cell thus produced, and axis-symmetrically aligning liquid crystal molecules by utilizing two-phase regions in which a liquid crystal phase and a uniform phase exist. This production method does not use alignment films.
(4) Furthermore, Japanese Laid-open Publication No. 6-308496 discloses a liquid crystal display device in a wide viewing angle mode including an axis-symmetrical alignment film made of a crystalline polymer with a spherulite structure on the surface of a substrate.
(5) Japanese Laid-open Publication No. 6-194655 discloses a technique for coating an alignment film on a substrate and aligning liquid crystal molecules in a random direction without performing an alignment treatment such as rubbing.
There are techniques for dividing pixels into a plurality of regions and aligning liquid crystal molecules in each region in such a manner that the viewing angle characteristics in each region compensate for each other. Examples of the method will be described below.
(6) Japanese Laid-open Publication No. 63-106624 discloses a method for dividing each pixel into regions and performing an alignment treatment such as rubbing so that the rubbing directions in the respective regions become different.
FIGS. 31 and 32 show a liquid crystal display device obtained by the above method, having wide viewing angle characteristics and being capable of obtaining a display with a satisfactory contrast. FIG. 31 is a schematic plan view of the liquid crystal display device, and FIG. 32 is a cross-sectional view taken along the E-Exe2x80x2 line in FIG. 31.
A pixel electrode (transparent electrode) 520 provided on each pixel, an alignment film 510, and a thin film transistor 513 driving the pixel electrode 520 are provided on one glass substrate 522 of the liquid crystal display device. A counter electrode (transparent electrode) 519 and an alignment film 509 are provided on the other glass substrate 521. The alignment films 509 and 510 are made of polyimide. A pixel B defined by the opposing transparent electrodes 519 and 520 is a square of 200 xcexcm, for example, and a plurality of pixels B are arranged in a matrix. A band-shaped spacer 523 made of polyimide is provided in a center portion of the pixel electrodes 520, as a result of which each pixel B is divided into regions I and II by the band-shaped spacer 523.
The regions I and II are formed as schematically shown in FIG. 33. The glass substrates 521 and 522 are respectively subjected to a rubbing treatment in the arrow directions as shown in FIG. 33. In the past, in the case of providing the regions I with an alignment regulating force, the substrate 521 is subjected to a rubbing treatment with the regions II covered with a resist. Similarly, in the case of providing the regions II with an alignment regulating force, the substrate 521 is subjected to a rubbing treatment with the regions I covered with a resist.
According to the above technique, the alignment directions of liquid crystal molecules in the respective regions have the same spiral-type twist direction but form different angles with respect to the surface of the substrates. Due to the difference in angle with respect to the surface of the substrates, the liquid crystal molecules rise in different directions under the application of a voltage. Therefore, in the case where light is incident upon the substrate in a direction tilted from a direction normal to the substrate, the optical characteristics of the respective regions compensate for each other. As a result, the viewing angle dependence under the application of a voltage is cancelled in the regions having different orientations in each pixel between the substrates. Thus, optical characteristics with less viewing angle dependence are obtained. In particular, even when a viewing angle is varied in gray scales, there will be no phenomenon of gray-scale inversion.
(7) As a technique for making an alignment direction of an alignment film different, Japanese Laid-open Publication Nos. 7-199193 and 7-333612 disclose a technique for forming unevenness having a tilt in each pixel, thereby making the direction in which liquid crystal molecules are tilted different depending upon the region in each pixel. According to this technique, a pretilt angle is varied on a regional basis due to the different tilt directions in each pixel, thereby making the direction in which the liquid crystal molecules are tilted different. Thus, the viewing angle characteristics of a liquid crystal display device are improved. Japanese Laid-open Publication No. 7-199193 also discloses a homeotropic liquid crystal display device which uses an n-type (xcex94xcex5 less than 0) liquid crystal material and a homeotropic alignment film, and in which liquid crystal molecules are aligned in a direction vertical to substrates when no voltage is being applied and tilted in a direction horizontal to the substrates under the application of a voltage.
(8) Furthermore, Japanese Laid-open publication No. 6-301036 has proposed a liquid crystal display device having wide viewing angle characteristics and being capable of obtaining satisfactory display quality. FIG. 34 is a perspective view showing an external appearance of the liquid crystal display device, and FIG. 35 is a schematic cross-sectional view thereof. The liquid crystal display device includes a liquid crystal layer 612 having vertically aligned liquid crystal molecules 612A between a pair of electrode substrates. Pixel electrodes 611 are provided on one substrate 610, and counter electrodes 613 are provided on the other substrate (not shown). Each counter electrode 613 has openings 614 corresponding to central portions of each pixel.
The liquid crystal molecules 612A in a region of a liquid crystal layer corresponding to the opening 614 are stable, being vertically aligned under the application of a driving voltage. The liquid crystal molecules 612A on the periphery of the region corresponding to the opening 614 are also stable in alignment due to the interaction with the liquid crystal molecules 612A in the region corresponding to the opening 614. As a result, the liquid crystal molecules 612A in each pixel are aligned so as to face the central portion of the pixel corresponding to the opening 614. Thus, if the opening 614 of each pixel is provided at the identical position (e.g., a central portion of each pixel), the liquid crystal molecules are aligned similarly in each pixel. Because of this, even if a disclination line is similarly generated in each pixel, roughness of a display can be prevented. In FIG. 35, the reference numerals 615 and 616 denote gate bus lines, and 617 and 618 denote homeotropic alignment films.
Liquid crystal display devices (e.g., TFT-LCD) have been widely used as flat displays. However, large TFT-LCDs of a 20-inch or more diagonal screen, whose application for wall mounting has been expected, have not been commercially available. In recent years, as a candidate for realizing a large display device, a plasma address LCD (PALC) disclosed in Japanese Laid-open Publication No. 1-217396 has received attention.
FIG. 36 shows a cross-sectional structure of a PALC. A PALC 700 includes a liquid crystal layer 702 between a pair of substrates 701 and 711. A plurality of plasma chambers 713 are disposed between the substrate 711 and the liquid crystal layer 702. Each plasma chamber 713 is defined by the substrate 711, a dielectric sheet 716 opposing the substrate 711, and partition walls 712 provided between the substrate 711 and the dielectric sheet 716. Gas (e.g., helium, neon, etc.) sealed in the plasma chamber 713 is ionized by applying a voltage across an anode 714 and a cathode 715 formed on the surface of the substrate 711 in the plasma chamber 713, whereby plasma discharge occurs.
A plurality of plasma chambers 713 extend in the shape of stripes in a direction vertical to the drawing surface of FIG. 36 in such a manner as to be orthogonal to transparent electrodes 705 provided on the surface of the substrate 701 on the liquid crystal layer 702 side. Compared with a simple matrix type liquid crystal display device, the transparent electrodes 705 correspond to display electrodes (signal electrodes) and the plasma chambers 713 correspond to scanning electrodes. The substrate 711, the dielectric sheet 716, the plasma chambers 713, etc. are collectively called a plasma substrate 710.
Referring to FIG. 37, the basic principle of the PALC 700 will be described. The plasma chambers 713 are successively turned on, and the gas in the selected plasma chamber 713 is ionized. As shown in FIG. 37, under the condition that the plasma chamber 713 is ionized, a charge, in accordance with a voltage supplied from the signal lines to the transparent electrodes 705, is accumulated and held on a reverse surface of the dielectric sheet 716 on the plasma chamber 713 side. Thus, a signal voltage supplied from the signal lines is applied to a region of the liquid crystal layer 702 positioned above the ionized plasma chamber 713. When the plasma chamber 713 is not ionized, the charge is not supplied to the reverse surface of the dielectric sheet 716. Therefore, the signal voltage is not supplied to the region of the liquid crystal layer 702 positioned above the plasma chamber 713. Thus, the plasma chambers 713 function as scanning electrodes in a simple matrix type liquid crystal display device.
As a technique for producing a display with a large screen, Japanese Laid-open Publication No. 4-265931 discloses a technique of forming a plasma chamber structure on a glass substrate by a printing method using glass paste.
Japanese Laid-open Publication No. 4-313788 discloses a structure in which transparent electrodes are patterned in a direction of plasma chambers. In this structure, even when a thick dielectric sheet is interposed between plasma chambers and a liquid crystal layer for the purpose of enhancing the strength of the dielectric sheet, charge is prevented from dispersing on the liquid crystal layer side to cause bleeding of a display.
The above-described techniques have respective problems. Hereinafter, these problems will be described.
In the conventional liquid crystal display device in an ASM mode, a liquid crystal material with a positive dielectric anisotropy xcex94xcex5 is used. In this display mode, as described above, liquid crystal molecules are axis-symmetrically aligned, so that outstanding display characteristics are obtained in an omnidirection. However, this liquid crystal display device has the following problems (1) to (4): (1) since this display mode is a normally white (NW) mode, a relatively high driving voltage is required for decreasing the light transmittance under the application of a voltage so as to obtain a high contrast; (2) in order to prevent light leakage when no voltage is being applied, it is required to prescribe an area of each light-blocking portion (e.g., a black matrix (BM)) to be large; (3) the liquid crystal display device in an ASM mode is difficult to produce, because a phase separation step requiring complicated temperature control is used for forming an ASM mode; and (4) since the liquid crystal display device in an ASM mode is difficult to produce, it is difficult to control the position of each central axis around which liquid crystal molecules are symmetrically aligned, the position of the central axis is varied depending upon the pixel, and the central axis is not positioned almost at the center of the pixel region; as a result, when the liquid crystal display device is observed in an oblique direction, a rough display with unsatisfactory quality is obtained.
Furthermore, in the liquid crystal display devices using a liquid crystal material with a positive dielectric anisotropy xcex94xcex5 as described in the above-mentioned (6) and (7), alignment directions of the liquid crystal molecules on the division lines become discontinuous under the application of a voltage, i.e., disclination lines are generated, causing the decrease in contrast ratio. Furthermore, in this liquid crystal display device, in order to produce a plurality of divided regions, a resist is coated onto an alignment film, followed by rubbing on a region basis. According to this method, the alignment film is exposed to a resist material, a developing solution, a release agent, etc. Therefore, ions contained in the resist, the developing solution, the release agent, etc., remain on the alignment film after the resist is peeled off. The remaining ions may have an adverse effect on the display characteristics by moving during the operation of the liquid crystal display device to deteriorate the charge-holding characteristics of the liquid crystal material and to cause a phenomenon such as an image burn-in. Furthermore, depending upon the kinds of the alignment film and the resist to be combined, the alignment film is damaged to lose an alignment regulating force. Thus, such a liquid crystal display device is low both in production efficiency and production stability.
Furthermore, in the liquid crystal display device described in the above (8), the liquid crystal molecules are axis-symmetrically aligned only in the opening of the counter electrode. More specifically, the liquid crystal molecules on the periphery of the pixel away from the opening are not axis-symmetrically aligned. Thus, the liquid crystal molecules are randomly aligned, which may cause a rough display. Furthermore, the positions or sizes of liquid crystal domains (regions where the alignment direction of the liquid crystal molecules are continuous, and disclination lines are not generated) are not defined, so that disclination lines cannot be prevented from being generated in pixels, particularly, causing a rough display in gray scales.
The PALC has the following problems. The PALC mainly uses a TN mode. When a TN mode in which display quality depends upon a viewing angle is applied to a display device with a large screen, even when an observer""s position is fixed, the viewing angle (a and b) is varied depending upon the position of a display screen to be observed, as shown in FIG. 38. Therefore, the display quality becomes unsatisfactory in the display screen.
In the case of the PALC in a TN mode, considering the viewing angle dependence of the TN mode, polarization axes of polarizing plates are set at 45xc2x0 from a crosswise direction on the display surface, thereby adjusting the sideward viewing angle characteristics seen by an observer in a satisfactory direction. In this case, at a portion such as an attachment surface between the plasma substrate and the thin glass sheet where the difference in refractive index is present, an attachment portion becomes visible due to the birefringence and the difference in refractive index of polarized light on the attachment surface, whereby light leakage, which is critical to a display, occurs in a crosswise direction.
The PALC uses a display mode using p-type liquid crystal material, such as a NW mode and a TN mode. In the PALCs in these display modes, a sufficient contrast ratio cannot be obtained. This is caused by the nonuniform voltage (electric field) applied to the liquid crystal layer due to the nonuniform plasma charge. In the NW mode using p-type liquid crystal (xcex94xcex5 greater than 0), particularly, a black level under the application of a voltage is decreased, resulting in a great decrease in contrast ratio.
A liquid crystal display device of the present invention includes a pair of substrates and a liquid crystal layer provided between the substrates, wherein liquid crystal molecules in the liquid crystal layer have a negative dielectric anisotropy, and the liquid crystal molecules are aligned in a direction substantially vertical to the substrates when no voltage is being applied and axis-symmetrically aligned in each of a plurality of pixel regions under application of a voltage.
In one embodiment of the present invention, a thickness (din) of the liquid crystal layer in the pixel region is larger than a thickness (dout) of the liquid crystal layer outside of the pixel region, and the device includes a homeotropic alignment layer in a region corresponding to the pixel region on a surface of at least one of the substrates on the liquid crystal layer side.
In another embodiment of the present invention, at least one of the substrates has convex portions defining the pixel region on a surface on the liquid crystal layer side.
In another embodiment of the present invention, the thickness of the liquid crystal layer in the pixel region is largest at a central portion of the pixel region and continuously decreases toward a peripheral portion of the pixel region.
In another embodiment of the present invention, the thickness of the liquid crystal layer in the pixel region is axis-symmetrically changed around the central portion of the pixel region.
In another embodiment of the present invention, the above-mentioned liquid crystal display device further includes a projection at the central portion of the pixel region, wherein the liquid crystal molecules are axis-symmetrically aligned around the projection under the application of a voltage.
In another embodiment of the present invention, a retardation dxc2x7xcex94n of the liquid crystal layer is in a range of about 300 nm to about 500 nm.
In another embodiment of the present invention, a twist angle of the liquid crystal layer is in a range of about 45xc2x0 to about 110xc2x0.
In another embodiment of the present invention, the above-mentioned liquid crystal display device includes a pair of polarizing plates disposed in crossed Nicols on both sides of the liquid crystal layer, and a phase difference plate having a relationship, in which a refractive index nx,y in an in-plane direction is greater than a refractive index nz in a direction vertical to a plane, is provided on at least one of the polarizing plates.
In another embodiment of the present invention, an axis-symmetrical alignment fixing layer which provides the liquid crystal molecules with an axis-symmetrical pretilt angle is further formed on a surface of at least one of the substrates on the liquid crystal layer side.
In another embodiment of the present invention, the axis-symmetrical alignment fixing layer contains a photocurable resin.
A method for producing a liquid crystal display device of the present invention includes the steps of: forming a homeotropic alignment layer on a pair of substrates, respectively; disposing a mixture containing a liquid crystal material having a negative dielectric anisotropy and a photocurable resin between the homeotropic alignment layers on the substrates; and curing the photocurable resin while applying a voltage higher than a threshold voltage of the liquid crystal material to the mixture, so as to form an axis-symmetrical alignment fixing layer providing the liquid crystal molecules with an axis-symmetrical pretilt angle.
In one embodiment of the present invention, the above-mentioned method further includes the step of forming convex portions defining pixel regions on a surface of at least one of the substrates before the step of forming the homeotropic alignment layers on the substrates.
A liquid crystal display device of the present invention includes: a plasma substrate having plasma chambers for performing plasma discharge; a counter substrate having signal electrodes; and a liquid crystal layer provided between the plasma substrate and the counter substrate, the device being driven by the signal electrodes and the plasma chambers, wherein liquid crystal molecules in the liquid crystal layer have a negative dielectric anisotropy, and the liquid crystal molecules are aligned in a direction substantially vertical to the substrates when no voltage is being applied and axis-symmetrically aligned in each of a plurality of pixel regions under application of a voltage.
In one embodiment of the present invention, a thickness (din) of the liquid crystal layer in the pixel region is larger than a thickness (dout) of the liquid crystal layer outside of the pixel region, and the device includes a homeotropic alignment layer in a region corresponding to the pixel region on a surface of at least one of the substrates on the liquid crystal layer side.
In another embodiment of the present invention, at least one of the counter substrate and the plasma substrate has convex portions defining the pixel region on a surface on the liquid crystal layer side.
In another embodiment of the present invention, the thickness of the liquid crystal layer in the pixel region is largest at a central portion of the pixel region and continuously decreases toward a peripheral portion of the pixel region.
In another embodiment of the present invention, the thickness of the liquid crystal layer in the pixel region is axis-symmetrically changed around the central portion of the pixel region.
In another embodiment of the present invention, the above-mentioned liquid crystal display device includes a pair of polarizing plates disposed in crossed-Nicols on both sides of the liquid crystal layer, a polarization axis of one of the polarizing plates being parallel to an extending direction of the signal electrodes or the plasma chambers.
In another embodiment of the present invention, an axis-symmetrical alignment fixing layer which provides the liquid crystal molecules with an axis-symmetrical pretilt angle is further formed on a surface of at least one of the plasma substrate and the counter substrate on the liquid crystal layer side.
In another embodiment of the present invention, the axis-symmetrical alignment fixing layer contains a photocurable resin.
A liquid crystal display device of the present invention includes: a pair of substrates and a liquid crystal layer provided between the substrates, wherein liquid crystal molecules in the liquid crystal layer have a negative dielectric anisotropy, and the liquid crystal molecules are aligned in a direction substantially vertical to the substrates when no driving voltage is being applied and axis-symmetrically aligned around an axis-symmetrical alignment central axis in each of a plurality of pixel regions under application of a driving voltage, and convex portions defining the pixel region are provided on a surface of at least one of the substrates on the liquid crystal layer side, and a treatment for controlling a position of the axis-symmetrical alignment central axis is conducted.
In one embodiment of the present invention, the above-mentioned liquid crystal display device includes a region in which the liquid crystal molecules keep a homeotropic alignment state under application of an axis-symmetrical alignment central axis forming voltage at each predetermined position in the plurality of pixel regions.
In another embodiment of the present invention, Sa is an area of the region in which the liquid crystal molecules keep a homeotropic alignment state under the application of the axis-symmetrical alignment central axis forming voltage, A is an area of the pixel region, and Sa/A satisfies the relationship 0 less than Sa/A less than 4%.
In another embodiment of the present invention, the above-mentioned liquid crystal display device includes an axis-symmetrical alignment central axis forming portion at a predetermined position in each of the plurality of pixel regions, and the axis-symmetrical alignment central axis of the liquid crystal molecules is formed corresponding to the axis-symmetrical alignment central axis forming portion.
In another embodiment of the present invention, Sb is an area of the axis-symmetrical alignment central axis forming portion, A is an area of the pixel region, and Sb/A satisfies the relationship 0 less than Sb/A less than 4%.
In another embodiment of the present invention, a thickness of the liquid crystal layer in the pixel region is larger than a thickness of the liquid crystal layer outside of the pixel region.
In another embodiment of the present invention, the thickness of the liquid crystal layer in the pixel region is largest at a central portion of the pixel region and continuously decreases from the central portion to a peripheral portion of the pixel region.
In another embodiment of the present invention, the thickness of the liquid crystal layer in the pixel region is axis-symmetrically changed around the central portion of the pixel region.
In another embodiment of the present invention, an axis-symmetrical alignment fixing layer is provided on a surface of at least one of the substrates on the liquid crystal layer side.
In another embodiment of the present invention, the axis-symmetrical alignment fixing layer contains a photocurable resin.
A method for producing a liquid crystal display device is provided. The device includes a pair of substrates and a liquid crystal layer provided between the substrates, liquid crystal molecules in the liquid crystal layer having a negative dielectric anisotropy, the liquid crystal molecules being aligned in a direction substantially vertical to the substrates when no driving voltage is being applied and being axis-symmetrically aligned around an axis-symmetrical alignment central axis in each of a plurality of pixel regions under application of a driving voltage. The method includes the step of performing an axis-symmetrical alignment central axis forming process.
In one embodiment of the present invention, the axis-symmetrical alignment central axis forming process includes the steps of: disposing a precursor mixture containing a liquid crystal material and a photocurable material between the substrates; and curing the photocurable material while applying an axis-symmetrical alignment central axis forming voltage to the precursor mixture.
In another embodiment of the present invention, the axis-symmetrical alignment central axis forming voltage is xc2xd or more of a threshold voltage of the liquid crystal material.
In another embodiment of the present invention, the axis-symmetrical alignment central axis forming voltage is an AC voltage.
In another embodiment of the present invention, a frequency of the AC voltage is 1 Hz or more.
Thus, the invention described herein makes possible the advantages of (1) providing a liquid crystal display device including a liquid crystal region in which liquid crystal molecules are axis-symmetrically aligned in each pixel region, having outstanding viewing angle characteristics in an omnidirection and a high contrast without roughness; (2) providing a plasma address LCD having outstanding viewing angle characteristics and a high contrast; and (3) providing a method for producing the liquid crystal display devices as described above with ease.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.